1. Field of the Invention
This invention relates to a light space-transmission device, and more particularly, is suitably applicable to, for instance, a light space-transmission device for enlarging the luminous-flux-diameter of the light beam by means of a light beam expander and for transmitting a light beam.
2. Description of the Related Art
A light space-transmission device has been conceived wherein information signals are transmitted via a light beam. In such a light space-transmission device, a laser diode is driven with the stated information signal, and the luminous-flux-diameter of a light beam that is emitted from the laser diode is enlarged by means of a light beam expander, and the light beam is transmitted to an opposed other light space-transmission device that is the partner of the communication. Then, the other light space-transmission device receives this light beam with a light receiving element, and demodulates the output signal of the light receiving element to obtain the information signal; in this way, the information signal is transmitted via the light beam. In the same way, information signals can be transmitted from the other light space-transmission device via light beams.
In such a light space-transmission device, it is required to perform optical-axis correction so as to match the optical axis of the light beam that is beamed toward the light space-transmission device of the partner to the light space-transmission device of the partner; various methods are conceivable for performing this optical-axis correction.
For instance, such an optical-axis correcting method can be conceived that the light space-transmission device is supported with a gimbal that is movable upwards, downwards, leftward and rightward and the direction of the entire light space-transmission device is varied; but, in this case, there are such problems that whole device becomes larger and more complex one, and the speed of response of the optical-axis correction becomes slower, because it is needed to move the entire light space-transmission device.
Besides, such a method for correcting the optical-axis of the light beam can be conceived that the light beam emitted from a light beam expander is reflected with a servo mirror, and the angle of this servo mirror is controlled; but, in this case, there are such problems that the reflecting surface of the servo mirror becomes larger, and the speed of response of the optical-axis correction becomes slower, because the servo mirror is required to reflect the entire light beam whose luminous-flux-diameter has been enlarged by the light beam expander.
Besides, such a method can be conceived that the optical axis of a light beam that is not yet thrown into the light beam expander is corrected by means of a servo mirror, and this light beam whose optical axis has been corrected is expanded with the light beam expander and then emitted. Referring to FIG. 1, a light space-transmission device generally designated as 1 is comprised of an optical block 10 for transmitting and receiving light beams, a light beam expander 30 for enlarging or diminishing the luminous-flux-diameter of the light beam, and a servo mirror 20 for controlling the angle of the optical axis of the light beam.
The light space-transmission device 1 receives a reception light beam L2 that comes from a light space-transmission device (not shown) of the partner with the light beam expander 30, diminishes the luminous-flux-diameter of the reception light beam L2 by the use of lenses 32 and 31, and sends it to the optical block 10 via a mirror 21 of the servo mirror 20.
In the the optical block 10, the reception light beam L2 is passed through a beam splitter M1, and then a part of the reception light beam L2 is reflected by a beam splitter M2 and brought into convergence on a position detecting element 13 via a lens 16; the rest of the reception light beam L2 is passed through the beam splitter M2, and converged on a light receiving element 12 via a lens 15. And, the light space-transmission device 1 performs photoelectric conversion of the converged reception light beam L2 into an electric signal by means of the light receiving element 12, and then decodes the electric signal with a signal processing circuit (not shown) of the subsequent stage, thereby restoring the information signal.
In transmitting light beams, the light space-transmission device 1 drives a laser diode 11 of the optical block 10 with the information signal that is supplied from the exterior, transforms a transmission light beam L1 that is emitted from the laser diode 11 into a parallel ray by means of a lens 14, reflects the transmission light beam L1 with a beam splitter M1, and further reflects the transmission light beam L1 with the servo mirror 20, so as to throw it to the light beam expander 30. The light beam expander 30 enlarges the luminous-flux-diameter of the transmission light beam L1 by the use of the lenses 31 and 32, and throws the transmission light beam L1 toward the light space-transmission device of the partner. In this manner, the light space-transmission device 1 transmits and receives the information signals through the medium of the transmission light beam L1 and the reception light beam L2.
At this time, the light space-transmission device 1 aligns the optical axes of the transmission light beam L1 and the reception light beam L2, so as to perform optical-axis correction for adjusting the optical axis of the transmission light beam L1 to the optical wireless device of the partner. The position detecting element 13 sends the light receiving position information of the reception light beam L2 at the light receiving plane of the position detecting element 13 to a controlling division (not shown). The controlling division calculates the difference between the actual light receiving position and the light receiving position (reference position) of the reception light beam L2 that is in such a state that the optical axes of the transmission light beam L1 and the reception light beam L2 have been aligned, drives the mirror 21 on the basis of this difference, and adjusts the light receiving position of the reception light beam L2 such that it coincides with the reference position, thereby achieving the optical-axis correction.
By locating the servo mirror 20 between the optical block 10 and the light beam expander 30, the mirror 21, as a result, the speed of response can be improved.
The angle of light which is emitted from the light beam expander becomes a value that is given by dividing the angle of the light thrown into the light beam expander by the enlargement ratio of the light beam expander. That is, as shown in FIG. 2, in the case where the angle of the mirror 21 is increased by a degree, the optical axis of the light beam that is thrown into the light beam expander 30 increases by 2xcex1 degrees, and, provided that the enlargement ratio of the light beam expander 30 is X, the change of angle of the optical axis of the light beam that is emitted from the light beam expander 30 becomes 2xcex1/X degrees. For instance, if the enlargements ratio of the light beam expander 30 is 16 times, and the optical axis correcting angle range that is required for the light space-transmission device 1 is xc2x11 degree, then xc2x18 degrees is required for for the rotational range of the mirror 21. In the case where the servo mirror 20 is placed between the optical block 10 and the light beam expander 30 in this way, such problems still exist that the required rotational-range of the mirror 21 becomes wider and, therefore, the servo mirror 20 becomes larger and more complex.
In view of the foregoing, an object of the invention is to provide a light space-transmission device which has a simple constitution and a wide range of optical-axis correction.
The foregoing object and other objects of the invention have been achieved by the provision of a light space-transmission device which has transmitting means for transmitting a light beam modulated with a predetermined information signal to another light space-transmission device spaced at a predetermined distance, light receiving means for receiving a transmission light transmitted from another light space-transmission device spaced at a predetermined distance as a reception light beam, a plurality of luminous-flux-diameter converting means for converting the luminous-flux-diameters of said transmission light beam and said reception light beam, optical axis correcting means for controlling the angle of the optical axes of said transmission light beam and said reception light beam.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like, are designated by like reference numerals or characters.